This invention relates to an improved array of inertial barriers of the type used alongside a roadway to decelerate a vehicle that has left the roadway.
Inertial highway barriers have been used for some time to prevent vehicles from striking an obstacle such as a bridge pier or the like at full velocity. An inertial barrier relies on the mass of the barrier to decelerate the vehicle. Typically, a dispersible material such as sand is enclosed in a frangible container. When the vehicle strikes the container, the momentum of the impacting vehicle is dissipated in accelerating the sand.
Early uses of inertial barriers are disclosed in Fitch U.S. Pat. No. Re 29,544 and Ford U.S. Pat. No. 4,183,504. In these barriers the mass of sand is elevated above the roadway on a platform in an attempt to match the heights of the centers of gravity of the barrier and the impacting vehicle. In this way, the tendency of the impacting vehicle to be accelerated vertically (either up or down) by the barrier is minimized. Later approaches have used other structures to elevate the center of gravity of the dispersible mass. For example, Seegmiller U.S. Pat. No. 4,073,482 discloses barriers having sand in a wine glass shape. Young U.S. Pat. No. 4,289,419 discloses an inertial barrier system wherein a central void is provided in the lower part of the barriers. Zucker U.S. Pat. Nos. 4,688,766 and 4,557,466 disclose inertial barriers wherein an insert is used to elevate the center of gravity of the lighter weight barriers.
In all of the inertial barriers discussed above, the more massive barriers include a substantially monolithic block of dispersible material. This configuration causes the mass per unit of height of the barrier to be relatively large. For this reason, a mismatch of only a few inches between the elevations of the centers of gravity of the barrier and the impacting vehicle can result in undesirably large vertical accelerations being imparted to the vehicle. Note for example the substantially solid masses of sand shown in the barriers of FIGS. 3a and 3b of the Zucker patents, in the 1400 pound barriers of the Young patent, and in all of the barriers of the Seegmiller, Fitch and Ford patents. This configuration can represent an unnecessary hazard to an impacting vehicle if the sand is wet and frozen. In this case, the monolithic block of sand is no longer easily dispersible, and it can cause unacceptably large decelerations to the vehicle. Additionally, unacceptably large blocks of frozen sand may be accelerated by the vehicle, and these accelerated blocks may present hazards to bystanders.
Of course, it should be recognized that not all highway barriers are inertial barriers. Another class of barriers relies on a fixed support for the barrier, and this support may be either horizontally or vertically oriented. Such barriers are secured to the support such that it is not the inertia of the barrier itself that provides the principal decelerating force. Note for example the energy absorbing devices shown in Walker U.S. Pat. No. 3,666,055, Meinzer U.S. Pat. No. 4,101,115, and Platt U.S. Pat. No. 3,141,655. Platt in FIG. 6 shows an energy absorbing device that includes an annulus of sand 28. The entire device is secured to a concrete base 14 by a tension rod 30. Because the Walker, Meinzer and Platt energy absorbing devices are not inertial barriers, they are of limited application to the present invention.
It is a primary object of this invention to provide an inertial barrier array that provides reduced vertical accelerations to an impacting vehicle, in spite of variations in the height of the center of gravity of the impacting vehicle.
It is a further object of this invention to provide an inertial barrier array which reduces or eliminates solid masses or discs of dispersible material extending completely across the barriers of the array.
It is yet a further object of this invention to provide an improved inertial barrier array in which each of the barriers of the array has improved water drainage characteristics.